Acoustic and photo-ID research on humpback whales (Megaptera novaeangliae)
Internship @ Sea Search Africa
During my internship with Sea Search Africa I worked on a set of photographic and acoustic data on humpback whales (Megaptera novaeangliae) collected late last year. The goal of the study was to collect sounds of animals known to be feeding in the large aggregations of whales, which occur off the west coast in late winter and early summer. This data will then be used to help us identify sounds made on moored hydrophones as part of the E3C project. The data was collected around Hout Bay in November 2015 over 6 days in collaboration with Steve Benjamin of Animal Ocean who took us out to sea when we didn’t have our own boat.
Photo-Identification (photo ID):
Photo-identification is the practice of identifying animals from their natural marks (fin shapes, scars, injuries, colouration etc) from photographs of them. Important for photo-ID of whales and dolphins are shots of the dorsal fin from both left and right sides and for humpback whales, the underside of tail fluke, which has individually distinctive black and white patterning.
My task was identifying all the individuals photographed over the 6 days by pulling out all the left dorsal fins (LD), the right dorsal fins (RD) and the tail flukes (TF). I identified every single individual and gave everyone a number and identified the ‘best’ image each side (and tail) of each whale for each day, essentially making three catalogues a LD (e.g. FIG. 2), RD (e.g. FIG. 1) and TF catalogue. I drew the different dorsal fins and tail flukes of the whales on paper and I also named a few of them to remember them better, which is pretty helpful during the identifying process. On the basis of the best pictures I matched the left and right dorsal fin together to one whale where possible.
Some of the pictures I turned into black and white, because it is easier to see marks and it also highlights the shape.
Matching the tail fluke to the right and left dorsal fin was the hardest part. The main identifying feature used is the under-side but by using the many different angles photographed it is often possible to match a ‘side shot’ as below to both a dorsal fin and a good underside (FIG. 3).
FIG. 3: pictures of the left dorsal fin, the right dorsal fin, the tail fluke in different perspectives and a “side-shot” of the whale WSAMN_006
There are now over 120 individuals in the photo-ID catalogue. I found over 30 matches of the right and left dorsal fin, nearly 20 matches all together (LD, RD, TF) and nearly 40 matches of the dorsal and tail fluke. Once complete, this catalogue will be compared to those from other research groups to contribute to a national level project.
I also did field work and it was pretty cool that I identified one whale which I saw on my first research trip, as a member of the catalogue. This whale was also seen in November and it has been hanging around the Hout Bay area for several months.
Humpback whales are known as the best singers in the ocean, but only the male whales sing. Most of the time they sing during mating season to attract female whales. But there are also social vocalizations produced by both male and female humpback whales which are heard on the feeding and breeding grounds and even surface-generated percussive sounds as breaches, pectoral flipper slaps and tail slaps (Dunlop R. A. et al., 2007).
During my internship, I did the first part of the acoustic analysis Adobe Audition. I converted the spectrograms to the right settings for viewing, noted the start and end time of each noise and quantified, classified and categorized the noises (mostly following the categories defined by Rebecca Dunlop and colleagues in Australia – Dunlop et al. 2007). All in all I found over 1500 sounds in the acoustic data of the first three days of research. Most of the sounds are between 100 Hz and 4 kHz and can be divided into low-, mid- and high-frequency sounds. Low frequency sounds are the most common, especially the “wop” (FIG. 4), “grumbles” (FIG. 5) and “barks” (FIG. 6). The most common mid-frequency sound is the “modulated cry” (FIG. 7) and the common high-frequency sound is the “shriek” (FIG. 8). For those who are interested in listening to some social sounds of humpback whales, here are some sound clips you can listen to (above is an example of the associated soundwave).